1. Field of the Invention
The present invention relates generally to a photometer, and more particularly, to a photometer employed in an optical device such as a camera.
2. Description of the Related Art
In these years, in photometer circuits of optical devices such as cameras, an incident light beam is converted to a photoelectric current by using a photodiode, and the photoelectric current is converted to a logarithmic compression voltage. Alternatively, the photoelectric current is accumulated in a capacitor for A/D conversion. In these cases, it is necessary to use diodes for compression and to use comparators and reference voltage generating circuits for A/D conversion, and bipolar ICs are employed.
On the other hand, processing circuits, such as exposure control circuits and display circuits, for receiving and processing outputs from the photometer circuits have been digitized for the reason of easy processing, and CPUs (Central Processing Unit) are used therefor. Accordingly, at least two types of ICs, i.e. bipolar ICs and CPUs, have been used for the photometer circuits and processing circuits of the optical device such as cameras.
However, it is disadvantageous, in terms of circuit dimensions and costs, to use such bipolar ICs and CPUs for photometry.
Further, CPUs which are manufactured by combining a bipolar process and a C-MOS process have been developed; however, the manufacturing process is complex and incurs high costs.